Electric power distribution panelboards, switchboards and busway are currently available which accept circuit breakers and electric switches by means of a plug-on connection to the bus bars arranged therein. U.S. Pat. No. 4,744,003 describes one such panelboard arrangement. When electric switches or circuit breakers are to be installed on-site within such an operating panelboard, switchboard or busway system the electric power must be temporarily discontinued and the panelboard or switchboard disassembled before such electric switch or circuit breaker can be installed. Where modifications must be made to the panelboard or switchboard interior in order to accept the electric switch or circuit breaker, some time is required before the power can be turned ON. This disruption in electric power within an industrial environment could cause scheduling problems both with respect to the related equipment as well as to operating personnel.
With same panelboard, switchboard and busway enclosures, it is often convenient to directly plug the electric switch or circuit breaker directly onto the edge-mounted electric bus bars with minor modification in which case the panelboard or switchboard must be de-energized to prevent damage to the equipment as well as to personnel. To deter electrical circuit with the bus bars in the event that the enclosure becomes inadvertently energized, some means should be employed to prevent direct access at all times to those bus bars that are not connected with the modular enclosures, electric switches or circuit breakers.
U.S. Pat. No. 4,754,247, entitled "Molded Case Circuit Breaker Accessory Enclosure", describes a circuit breaker having an electronic trip unit and accessory devices mounted within the circuit breaker cover and accessed by means of an accessory cover without affecting the integrity of the circuit breaker case which contains the circuit breaker operating components such as the operating mechanism, contacts and arc chute. A wire access slot formed within the circuit breaker case allows for the egress of the wire conductors leading to the accessories while an arc vent slot formed within the circuit breaker case adjacent the arc chute provides supplemental gas venting to the arc gases that are generated during circuit interruption. When such side-vented circuit breakers are used within the panelboards, switchboards and busway systems containing the edge-mounted bus bars, the bus bars should be shielded from direct contact with the arc gas by-products that accompany the arc gas evolution from the vent slot.
U.S. Pat. No. 5,067,043 describes a plurality of insulation seals positioned over the exposed bus bars within panelboards and switchboards containing the edge-wise mounted bus bars to shield the bus bars from the gaseous by-products issuing from the circuit breakers during intense circuit interruption. Similarly, the bus bars and tab connections of the busway are insulated to shield the bus bars from the gaseous by-products.
The so-called "current limiting" circuit interruption accomplished within the circuit breakers described within the aforementioned U.S. Pat. No. 4,754,247 interrupts the circuit current in the early stages of the current waveform in order to limit the let through current to a reasonable value. However, such rapid circuit interruption results in an intense arc discharge that must be rapidly cooled and quenched within the circuit breaker arc chute in a relatively short period of time.
It would be economically advantageous to provide a so-called "arc proof" circuit breaker whereby the hot gases generated during the circuit interruption process are prevented from exiting in the direction of the electrical distribution power connections at the line end of the circuit breakers.
Accordingly, one purpose of the invention is to describe an inexpensive, arc-proof circuit breaker usable within panelboards, switchboards and busway systems without requiring that the associated edge-mounted bus bars be separately shielded.